Improvement of the desorption of the herbicide norflurazon from soils via complexation with β-cyclodextrin

The effect of β-cyclodextrin (β-CD) on the removal of the herbicide norflurazon (NFL) from soils has been investigated. The interaction of NFL with β-CD in solution yielded the formation of a water-soluble inclusion complex at 1:1 stoichiometric ratio, which gave an increase in NFL solubility. Desorption studies of NFL previously adsorbed on six soils of different characteristics have been performed in the presence of 0.01 M β-CD or 0.01 M Ca(NO3)2 as extractant solutions. Positive hysteresis was observed in all soils when 0.01 M Ca(NO 3)2 solution was used, indicating that desorption of NFL from these soils was not completely reversible. On the contrary, the application of β-CD solutions to soils where NFL had been previously adsorbed increased very much its desorption, and a negative hysteresis was obtained for all soils studied; that is, more NFL was desorbed with respect to NFL adsorption isotherm. A clear relationship was observed between the physicochemical characteristics of the soils and the β-CD concentration necessary to remove the herbicide, the percentages of desorption observed for each soil being inversely related to the values obtained for the Freundlich sorption capacity parameter of the herbicide, Kf. In general, high desorption yields can be obtained with very low β-CD concentrations, which is an important advantage from an economic point of view, although in those soils that present an extremely high NFL adsorption, higher amounts of β-CD should be used. The results obtained indicate the high extracting power of β-CD toward the herbicide previously adsorbed on the soils and the potential use of β-CD for in situ remediation of pesticide-contaminated soils.

Peer Reviewed